When Mia Macy (pictured far left with her wife Tracy) was passed over for a position at the Bureau of Alcohol, Tobacco, Firearms, and Explosives, that she said had been promised was hers, the Phoenix police detective’s investigative prowess kicked in.

More than a year ago, Macy, who is transgender, had contacted the director of an ATF crime laboratory in Walnut Creek, Calif. about an open position as a ballistics forensic technician. At the time, she presented herself as a man. But Macy soon informed the hiring agency that she was transitioning from male to female. Five days later, she was told the Walnut Creek position had been eliminated due to federal budget cuts.

Only it hadn’t. Someone else had been hired for the job, and Macy suspected she had been dropped from consideration after revealing she was transgender. She filed a complaint in June 2011 with the U.S. Equal Employment Opportunity Commission, claiming that she was discriminated against on the basis of her gender identity.

Now, in a decision described by Macy’s attorney as “game-changing,” the EEOC has ruled that Title VII of the Civil Rights Act protects transgender individuals from sex discrimination.

Title VII does not simply prohibit discrimination based on biological sex, the EEOC, an independent agency that enforces federal workplace discrimination laws, ruled in a 16-page decision issued April 20.

Rather, the law’s “protections sweep far broader than that, in part because the term 'gender' encompasses not only a person’s biological sex but also the cultural and social aspects associated with masculinity and femininity,” the commission ruled. Macy’s case has now been remanded for further investigation.

The EEOC decision confirms a trend in federal court decisions interpreting Title VII to protect transgender individuals from sex-based discrimination.

“This decision is going to be game-changing for transgender people who face employment discrimination in this country,” said Ilona Turner, legal director for the San Francisco-based Transgender Law Center, which represents Macy. “It’s precedent-setting, and it’s a binding decision on EEOC offices across the country.”

Macy, an Army veteran who now lives in the Bay Area with her wife, Trish, struggled to find work after she was denied the ATF position, applying for more than 300 jobs but finding few leads, given her narrow detective expertise. Reached by phone, Macy said the EEOC’s historic decision in her case had yet to sink in. “I just never thought I’d be holding a piece of paper like that,” she said of the ruling she received in the mail. “It’s amazing, and it’s not about me. It means that everyone will get an equal investigation, that you’ll be part of the normal process.”

Advocates hailed the decision as a significant victory for transgender individuals who face extreme and pervasive workplace discrimination throughout the country. The ruling could also serve to boost efforts to bar federal contractors from discriminating against LGBT individuals. Earlier this month, that push hit a snag when the White House announced it would not be pursuing an executive order prohibiting sexual orientation and gender identity discrimination for such contractors.

National Center for Transgender Equality executive director Mara Keisling congratulated the Transgender Law Center and said in a statement on the ruling, “[T]his is a major victory. As many as 90% of trans people still face tremendous discrimination in employment according to our National Discrimination Survey, and it will help so much that the EEOC agrees with what more and more courts have been saying, that discriminating against trans people because of their sex, or their perceived sex, or what an employer thinks about their sex is clearly sex discrimination, illegal and wrong."

Tico Almeida, founder of Freedom to Work, a group pushing for employment protections for LGBT Americans, said Tuesday that the EEOC decision should be swiftly applied to all federal agencies and called on Secretary of Labor Hilda Solis to issue new guidelines for federal contractors to protect against anti-transgender discrimination. Almeida’s group, as well as organizations such as the Human Rights Campaign and the Center for American Progress, have pushed the White House for an executive order applying to federal contractors that bars anti-LGBT discrimination.

“There is no need for Secretary Solis to wait for President Obama to fulfill his campaign promise to sign such an executive policy because the EEOC has just given the Labor Department the legal reasoning and authority to interpret the existing executive order, created by President [Lyndon B.] Johnson many decades ago, to now protect transgender Americans,” Almeida said in a statement.

“Unfortunately, Secretary Solis will not have the legal authority to protect gay and lesbian Americans from discrimination at federal contractors until President Obama corrects the mistake announced by White House staff a few weeks ago and issues a new executive order banning workplace discrimination based on sexual orientation,” he continued. “Gay and lesbian Americans who face prejudice and harassment in the workplace of federal contractors should not have to wait on the President any longer.”